You might want to have a look through Dan's videos and also find him on Facebook as he's an Englishman detecting in Germany. He has lots of experience with detecting WWII-era sites and could probably answer a few of your questions. I do not think that detecting the place should be completely frowned upon by others provided that respect is shown, given the context. People will always find this a troubling area of history as, for some, it is still in living memory. However, in terms of landowner's permission, without it you are breaking the law. Trespass is trespass. If I were you I'd find land elsewhere, above board and not damage the reputation of detectorists. Just my tuppence worth. Good luck with whatever you decide.